It is known to use a single-cylinder SCBA as an escape breathing apparatus, allowing a user to escape from environments that pose an Immediate Danger to Life or Health (IDLH). See the Premaire.RTM. Cadet Respirator made by the Mine Safety Appliances Company (MSA) of Pittsburgh, Penn. (MSA Data Sheet No. 01-00-04). Generally, such single-cylinder SCBA's used as an escape breathing apparatus employ air cylinders which provide a minimum air supply of five minutes up to a maximum air supply of about ten minutes. The actual duration of the air supply in a particular situation varies according to a number of factors, such as age, weight, physical condition, and breathing rate of the user of the SCBA. It is generally understood that five to ten minutes of air supply is sufficient time for escape from most environments likely to be encountered by a user of an escape breathing apparatus. Nonetheless, in certain situations it would be desirable to increase the air supply of an escape breathing apparatus to greater than ten minutes.
It is known to use an SCBA having a single air cylinder as an entry or escape device provided it has more than a fifteen minute supply of air. See the TransportAire.TM. Portable Air Supply System from MSA (Data Sheet No. 01-05-02). A minimum air supply of fifteen minutes is required for an SCBA to be approved by the National Institute for Occupational Safety and Health (NIOSH) for use for both entering and escaping IDLH environments. Such single-cylinder SCBA's, however, are generally too large and bulky to be worn in certain IDLH environments such as confined spaces.
It is also known to use an SCBA having multiple small air cylinders for use as an entry or escape breathing device which provide more than a fifteen-minute air supply. Such a product is made by Respiratory Devices, Inc. and is sold under the trademark Lifeair. There are certain disadvantages inherent in the design and construction of such SCBA's which become apparent when these devices are used in certain IDLH environments such as confined spaces.
Generally, these dual-cylinder SCBA's have a forged, rigid connection between the air cylinders which also serves as the air manifold. The rigid metal manifold also produces an SCBA with a higher profile than desired for maneuvering in confined spaces. Moreover, such a rigid connection dictates a placement of the pressure gauge and valve wheel where they are susceptible to being damaged or rendered inoperable if the unit is dropped or struck such as is likely to occur in a confined space. In addition, the necks of the air cylinders of these SCBA's are less capable of accepting shock loading without over-stressing due to the rigid manifold connecting the air cylinders.
It would be desirable to have a light-weight, lower-profile SCBA having multiple small cylinders which can provide an air supply of at least fifteen minutes for use in both entering and escaping from an IDLH environment and particularly one in a confined space.
It would also be desirable to have a multi-cylinder SCBA wherein substantially all of the high pressure operating components, such as the pressure gauge, cylinder valve and wheel, pressure relief rupture disk, high pressure regulator and low-pressure alarm could be located substantially within the envelope created by the cylinders, where such components are much less susceptible to being damaged or rendered inoperable if the unit is dropped or bumped.